The present invention relates to an inclined screen tray tower having one or more inclined screen trays, whereby liquid is directed onto the screen tray to form a film of the liquid on each of screens and gas is passed through the liquid films. so as to be absorbed by the liquid.
In order to obtain improved gas absorption rates, packed towers have come into wide use in place of spray towers and the like. To obtain an improved gas-liquid contact efficiency, it has been the general practice to use as the packing any material having a large void volume, low resistance to gas flow and less tendency to cause deflections. With the packed towers of the type used for treating gas containing dust, etc., however, when the tower is operated for a long period of time, the packing will be clogged with the dust thus increasing the resistance to the gas flow within the tower and thereby causing a power loss, and eventually a point will be reached where the operation must be stopped to perform a packing cleaning operation or to remove, in extreme cases, the packing from the tower for cleaning.
To overcome these deficiencies, inclined screen tray towers have been proposed and used as absorption towers in which one or a plurality of stages of screen trays are provided, whereby liquid is directed downwardly onto the screen tray to form a film of the liquid on each screen and gas is passed upwardly through the liquid films to cause the liquid to flow, being bubbled by gas, along the surface of the inclined screens, thus increasing the gas-liquid contact efficiency. It has been proved that a tower of this type has an improved rate of absorption. With the tower of this type, for example, the angle of inclination of 5.degree. to 20.degree., and screens of 5 to 20 meshes according to the Tyler standard screen scale have been proposed for the screen tray of the tower. With this tower, the angle of inclination and the screen opening of the screen tray are dependent on the type and flow rate of liquid and gas and the ratio between the flow rates. It is possible to obtain a satisfactory flow condition of liquid by suitably selecting the angle of inclination and the screen opening for the screen tray.
Even with this tower which is capable of ensuring a satisfactory flow condition of liquid with respect to certain design values, a variation in the amount of gas or liquid quantity tends to deteriorate the liquid flow condition and thereby to make it impossible to obtain the desired absorption efficiency. In other words, the ranges of flow rate of gas and liquid which are capable of ensuring a satisfactory flow condition of liquid and improved absorption efficiency are extremely narrow and limited.
Whilt it is considered that the range of tower operation can be increased by decreasing the screen opening, it is a disadvantage that a reduction in the screen opening tends to cause clogging of the screens with dust. On the other hand, while the screen opening must be increased to increase the flow rate of gas and thereby to increase the operating efficiency of the tower, if the screen opening is increased, the liquid will no longer be held in flowing condition bubbled by gas on the screens, causing the liquid to pass downwardly through the screens and thereby making it impossible to ensure a satisfactory absorption. To overcome this disadvantage, a method has been proposed in which a like screen is provided at a height of about 50 mm from the screens to provide a double-structure screen tray, and this method is also disadvantageous in that the construction is complicated, that the dust contained in gas tends to deposit and clog the packing layers and so on.